Process for the liquid phase direct oxi-
dation of olefins to olefin oxides



United States Patent "ice 3,281,433 PROCESS FOR THE LIQUID PHASE DIRECTOXI- DATION 0F OLEFINS TO OLEFIN OXIDES Stanley L. Reid, St. Louis, Mo.,assignor to Monsanto Company, a corporation of Delaware No Drawing.Filed Aug. 20, 1962, Ser. No. 218,113 8 Claims. (Cl. 260-3485) Thisinvention is directed to a new and improved process for the preparationof olefin oxides. It is further directed to an improved solvent for useas an oxidation medium for the preparation of olefin oxides by theaction of molecular oxygen upon olefins.

Still more particularly this invention relates to a process for thedirect epoxidation of olefins with molecular oxygen in a solventcomprising certain esters of benzoic acid.

Olefin oxides are extremely useful articles of commerce. They are usedas starting materials for the preparation of anti-freeze compositions,humectants, pharmaceutical preparations, cosmetic formulations, asmonomers for the preparation of polymers useful in preparingpolyurethanes, and the like. Notable among these epoxides are ethyleneoxide and propylene oxide. Currently these are prepared by a vapor phasecatalytic method and by the classic two-step chlorohydrin .route,respectively. The vapor phase process insofar as industrial productionof epoxides is concerned, is apparently confined to the preparation ofethylene oxide. Higher olefins have yet to be used in a vapor phasecatalytic process to give economic production of the correspondingoxides. The older chlorohydrin route is the principal industrial processwhich supplies the largest quantities of propylene oxide for commerce.This process is suitable for conversion of ethylene and propylene totheir corresponding epoxides, but higher olefins are not particularlyadaptable to the chlorohydrin route.

Still a third process for the preparation of olefin oxides is thatinvolving peracetic acid oxidation of olefins to the correspondingoxides. This process appears to have wider application insofar as olefinstructure is concerned than do the first two methods mentioned. Itapparently proceeds by an ionic mechanism, and the rate of epoxidationusing peracetic acid is characteristic of the structure of the olefin.Highly substituted ethylenes, for example tetramethylethylene andtrimethylethylene, react smoothly and rapidly with peracetic acid togive the corresponding epoxides. However, ethylenic compounds havingmuch lower degrees of substitution about the ethylene group, forexample, ethylene and propylene, by virtue of the ionic nature of thereaction, react sluggishly with peracetic acid and the rate of formationof the corresponding epoxides is very slow.

Nevertheless, each of these aforementioned processes has inherentdisadvantages. For example, vapor phase catalytic oxidation of ethyleneto ethylene oxide requires large volume equipment and the handling oftremendous quantities of potentially explosive mixtures of ethylene andoxygen. The second process, that is, the chlorohydrin route, forpropylene oxide essentially involves a two-step process; in addition,chlorinated byproducts arise in this process. The third process,involving peracetic acid oxidation of olefins, is potentially hazardousif relatively large quantities of peracetic acid are to be used. It isnoted, however, that the peracetic acid process is probably the mostversatile of the three methods; it is applicable to a far greater rangeof olefin structures than is the vapor phase catalytic process or thechlorohydrin process.

There are scattered references to still a fourth method of preparingolefin oxides, namely the liquid phase oxidation of olefins withmolecular oxygen. Several of these 328L433 Patented Get. 25, 1966 arerestrictive in the sense that specific limitations are incorporated ineach method. For example, catalysts or other additives or secondarytreatment of the oxidation mixtures with basic materials are essentialfeatures of these methods.

Since the present invention is concerned with a novel liquid phaseepoxidation system, the discussion below will be directed to typicalexisting prior art schemes for liquid phase olefin oxidations. Theseprior art processes describe a variety of approaches to a properbalancing of a series of reaction variables in order to obtain thedesired olefin oxide. For example, various specific oxidation catalystsor catalyst-solvent systems have been described (U.S. Patents 2,741,623,2,837,424, 2,974,161, and 2,985,- 668); another approach is theincorporation of oxidation anticatalysts which retard certainundesirable side reactions (U.S. Patent 2,279,470); still anotherapproach emphasizes the use of water-immiscible hydrocarbon solventsalone, or in the presence of polymerization inhibitors such asnitrobenzene (U.S. Patent 2,780,635) or saturated hydrocarbons (U.S.Patent 2,780,634); another method describes the use of neutralizers suchas alkali metal and alkaline earth metal hydroxides, or salts of thesemetals (U.S. Patent 2,838,524); another approach involves the use ofcertain catalysts in an alkaline phase (U.S. Patent 2,366,724), or aliquid phase maintained at specified critical pH values (U.S. Patent2,650,927); and still other approaches emphasize criticality of oxygenpressure (U.S. Patent 2,879,276), or the geometry of the reaction zone(U.S. Patents 2,530,509 and 2,977,374). The foregoing represent priorart approaches to problems encountered in the utilization of a liquidphase oxidation process to obtain olefin oxides.

It is the primary object of the instant invention to provide a superiorprocess for commercial production of olefin oxides which process is freeof numerous limitations recited in prior art processes.

A further object of this invention is to provide a liquid phase processfor the production of olefin oxides which is not dependent upon thepresence or absence of any catalyst; nor dependent upon thewater-immiscibility of solvents or upon solvents containing addedbuffers or acid neutralizers or other additives or secondary treatmentswith alkaline materials to remove acidic components; nor is it dependentupon the presence of saturated compounds, initiators or anticatalysts;further it is not dependent upon critical reactor geometries,temperatures, pressures, pH level, oxygen concentration flow rates, orreactant ratios.

It is a further object of this invention to provide a new class ofsolvents for direct epoxidation of olefins with molecular oxygen.

It is an additional object of this invention to provide a new processwhich is applicable to a wide range of olefin structures; that is, it isnot limited to a single olefin or two, but rather, has a broadapplication over a large class of unsaturated compounds.

It is an additional object of this invention to provide a new processwhich requires relatively small scale equipment and does not involve thehazards associated with certain of the prior art processes, e.g., thevapor phase process.

Other objects of this invention are to provide a process for theproduction of olefin oxides in batch or continuous manner by a methodwhich is simple, safe, economical and dependable.

These and other objects of the invention will become apparent to thoseskilled in the art as description of the invention herein proceeds.

According to the present invention, it has been discovered that olefinscan be oxidized to epoxides with molecular oxygen in high conversionsand yields when the oxidation is allowed to proceed-in a liquid reactionmedium comprising at least one benzoic acid ester having the followinggeneral formula:

wherein R R and R represent hydrogen, straight chain alkyl or haloalkylgroups having from 1-4 carbon atoms, or straight chain alkyl orhaloalkyl groups of from 14 carbon atoms having as substituents on otherthan the terminal carbon atoms thereof at least one member selected fromthe group consisting of straight and branched chain alkyl or haloalkylgroups having from l-4 carbon atoms.

Of the benzoic acid ester solvents disclosed herein, the most preferredmembers are methyl, ethyl and isopropyl benzoates because of their caseof preparation and ready availability.

Still other solvents within the above formula which are suitable hereinare the following benzoic acid esters: ethyl benzoate, n-propylbenzoate, butyl benzoate, t-butyl benzoate, 1,1dimethylpropyl benzoate,1,1-diethylpropyl benzoate, 1,1-dibutylpentyl benzoate,1,1-dimethylbutyl benzoate, 1,l,3,3-tetramethylbutyl benzoate,1,1-dirnethyltrichloroethyl benzoate, l,1-dimethyl-3-fluorobutylbenzoate, 2,2,2-trichloroethyl benzoate, 2-fluoroet hyl benzoate,2,3-dichloropropyl benzoate, 2-methyl-2,3-dichlorobutyl benzoate,2,3-di(trichloroethyl)butyl benzoate, and the like. In addition toindividual benzoic acid esters, mixtures of these esters in varyingproportions are also suitably employed as oxidation solvents accordingto the present invention. For example, a 50-50 weight percent of methylbenzoate and isopropyl benzoate is a desirable mixture.

These benzoic acid ester solvents are readily prepared by conventionalmethods such as by reacting benzoic acid with the correspondingmonohydric alcohol of the desired ester, in the presence of acidcatalysts; reacting benzoyl chloride with the corresponding alcohols inthe presence of basic materials; reacting benzoic anhydride with thecorresponding alcohols in the presence of acid catalysts; reactingbenzoic acid and the corresponding alcohol in the presence of an acidcatalyst and water entrainment, i.e., azeotroping agents; reactingsodium benzoate, or other metal-benzoate salt, with the halogenderivative corresponding to the alcohol desired, and the like.

The solvents used in the present invention combine essentialcharacteristics and features required for successful solution or liquidphase oxidation, that is, they are essentially chemically indifferentand are oxidatively and thermally stable. Furthermore, the instantsolvents are superior to those disclosed in prior art liquid phaseolefin oxidation processes in that they do not require buffers,neutralizers, initiators, polymerization or oxidation inhibitors and/orcatalysts in order to utilize the abovementioned essentials to effectoxidation of the olefin to the olefin oxide in high yield andconversion. Solvents of prior art processes require buffers,neutralizers, initiators, inhibitors and/or catalysts in order topromote the oxidation of the olefin and combat the deleterious effectsof by-products such as acidic components.

It is known that olefin oxidations give, in addition to epoxides,various by-products such as water, formic acid and acetic acid which canbe deleterious to the oxidation when present in appreciable quantitiesby reacting with the olefin oxide to give corresponding glycol andglycol derivatives as well as undesired polymeric materials. Prior artmethods have used a variety of approaches to counteract thesedeleterious effects, such as the use of water-immiscible hydrocarbonsolvents containing inhibitors or utilized in conjunction with aseparate washing step with solutions of basic substances, in effect,processes which require acid removal in order for such water-immisciblehydrocarbon solvents to be used for the olefin oxidation.

Probably the most deleterious constituent is formic acid which by virtueof its strong acidity (stronger than acetic acid by a factor of 10)reacts with the desired olefin oxide to form undesirable by-products. Ithas been found that acetic acid, unlike formic acid, can be tolerated inthe reaction mixture in much greater amounts than formic acid withoutproducing any adverse effects. One way to remove the reactive formicacid from the reaction mixture is by salt formation, that is, byaddition of an organic or inorganic base. However, these basic compoundsare known to inhibit primary oxidation reaction and therefore cannotsuitably be used. The formation of salts likewise presents additionalmechanical problems due to a build-up thereof in the reactor and saltremoval systems must be restorted to.

A feature of the present invention is the scavenging of the deleteriousformic acid as it is produced in the reaction through the use of anester of the class described herein, such as methyl benzoate. Anadvantage of using these esters as an acid scavenger is that a stableneutral material, i.e., the ester, is used to remove the strong formicacid by ester interchange and at the same time yield relativelyinnocuous products.

It is a primary feature of the instant invention that the benzoic acidester solvents need no added substances to counteract the deleteriouseffect of water and acids. Since the solvents used herein for the olefinoxidation are waterimmiscible, water and water-soluble acids formed inthe reaction are removed as a separate layer from the benzoic acid estercontaining the olefin oxide. Moreover, by use of the instant solvents asurprisingly substantial quantity of water and organic acids can betolerated without undue adverse effects upon the course of the olefinepoxidation.

It is a further feature of the instant invention that the olefinoxida-tions proceed at such a rapid rate that the oxygen isquantitatively consumed, hence, accumulation of potentially hazardousexplosive mixtures of oxygen and organic materials in the vapor stateare avoided.

It is further apparent that there is no criticality insofar as pH valuein concerned for this oxidation since appreciable concentrations of acidby-products, for example, up to 20 weight percent of acetic acid is notparticularly deleterious. Hence, the olefin oxidation in the presentsolvents proceeds suitably over a range of pHs as low as .pH 4 and inneutral and alkaline pH ranges.

Substantial evidence exists that these olefin oxidations, for example,propylene to propylene oxide by direct oxidation with molecular oxygenare propagated by a free radical chain mechanism. Copper and itscompounds are strong inhibitors for this propylene oxidation; aninhibition probably due to a redox reaction of copper with peroxyradicals which interrupts the chain propagation sequence and preventsattainment of a long kinetic chain necessary for reasonable conversionof the olefin. In addition, when free radical inhibitors, that is,antioxidants are added to the reaction mixture, partial or completeinhibition of the olefin oxidation occurs. In the absence of suchinhibitors a very rapid, vigorous exothermic oxidation of the olefinoccurs in the solvent. Furthermore, the present solvents are apparentlyvery resistant to free radical attack and are recovered substantiallyunchanged. On the contrary, among prior art solvents benzene is anexample of a compound which is readily attacked by free radicals. Such abenzene radical can react with oxygen to give phenolic orquinon-oid-type molecules which are known to be efficient inhibitors forradical chain oxidations, Thus, when benzene is used as a solvent for anolefin oxidation its susceptibility to free radical attack gives rise toan effect which might be termed auto-inhibition, that is, the rate ofoxidation of the olefin decreases with time. In contrast, the benzoicacid ester solvents have a high order of resistance to radical attackwhich can apparently be attributed to a stabilization of the phenylgroup by the carboxylate group toward radical attack such that theseesters do not impede the radical chain sequence, via an auto-inhibitioneffect which seems to operate when unsubstituted phenyl, i.e., benzene,is employed as solvent. In the instant benzoate ester solvents, theoxidation proceeds to the depletion of either olefin or oxygen.

The benzoic acid ester solvents used in the instant invention constitutea suitable reaction medium for substantially all ole-fin oxidations withmolecular oxygen to form olefin oxides. The term molecular oxygen asused herein includes pure or impure oxygen as well as gases containingfree oxygen, for example, air.

Olefins suitable for use herein preferably include those of theethylenic and cycloethylenic series up to 18 carbon atoms per molecule,e.g., ethylene, propylene, butenes, pentenes, hexenes, heptenes,octenes, nonenes, dodecenes, pentadecenes, heptadece-nes, octa'decenes,cyclobutenes, cyclopentenes, cyclohexenes, cyclooctenes, etc. Ofparticular interest, utility and convenience are the olefins containingfrom 2 to -8 carbon atoms. Included are the alkyl-substituted olefinssuch as Z-methyl-l-butene, 2- methyl-Z-butene, Z-methylpropene,4-methyl-2-pentene, 2- ethyl-B-methyl-kbutene, 2,3di-methyl-2-butene and2- methyl-Z-pentene. Other suitable olefinic compounds includebutadiene, isoprene, other pentadienes, hexadienes, heptadienes,octadienes, decadienes, octadecadienes, alkyl and polyalkyl-substitutedcycloalkenes and cycloalkadienes, vinyl-substituted cycloalkenes andbenzenes, cyclopentadiene, dicyclopentadiene, styrene, methylstyrene,alkylmethyl-styrene, and other vinyl-substituted aromatic systems.Another class of olefinically unsaturated compounds Which are ofinterest in this direct epoxidation to epoxides are the unsaturatedmacromolecules, that is, the rubbers, such as butadiene polymers,isoprene polymers, butadiene-styrene copolymers, isobutylene-isoprenecopolymers, chloroprene polymers and other copolymers incorporatingdienic and vinylic comonomers therein, and the like.

Particularly suitable olefin feed stocks contemplated in the instantinvention include the pure olefin or mixtures thereof or olefin stockscontaining as much as 50% of saturate-d compounds. Olefinic feedmaterials include those formed by cracking petroleum stock such ashydrocarbon oils, paraffin Wax, lubricating oil stocks, gas oils.kerosenes, naphthas and the like.

The reaction temperatures used in liquid phase olefin oxidations usingthe solvents of the instant invention are subject only to a lower limitbelow which the oxidation either proceeds too slowly or follows a courseother than that leading to olefin oxides. The upper limit of thetemperature range is that which may be termed a threshold above whichsubstantial decomposition, polymerization or excessive oxidative sidereactions occur, thereby leading to undesirable side reactions andproducts which substantially detract from the yield of the olefin oxide.In general, temperatures of the order of 50 C. to 400 C. arecontemplated. It is expedient to maintain temperatures at a sufficientlyhigh level to insure thermal decomposition of hazardous peroxide whichmay be formed and accumulated to the point of unsafe operation. Withinthis general temperature range preferred temperatures are within therange of 140-250 C.

Subatmospheric, atmospheric or superatmospheric pressures are suitablefor use in the instant invention, that is, ranging from 0.5 to 150-atmospheres. Usually the oxidation reaction is facilitated by the use ofhigher pressures, hence a preferred pressure range is from 10 to 100atmospheres. Pressures herein delineated and temperatures describedpreviously will generally be selected, of course, depending upon thecharacteristics of the individual olefin which is to be oxidized to theolefin oxide, but this combination of temperatures and pressures will besuch as to maintain a liquid phase. Olefin oxidations in the instantsolvents are autocatalytic, that is, they proceed by free radical chainreaction mechanisms, and the reactions proceed very rapidly after abrief induction period and give remarkably constant product compositionover wide variations of conditions. A typical olefin oxidation, forexample, propylene in batch operation, requires from about 1 to 20minutes. Similar, or faster, reaction rates occur in continuousoperation. The reaction vessel for conducting this olefin oxidation canbe made of materials which may include almost any kind of ceramicmaterial, porcelain, glass, silica, various metals, such as stainlesssteels, aluminum, silver and nickel, which vessels do not necessarilyhave to conform to any particular geometric design. It should be notedin the instant invention that no added catalysts are necessary and noreliance is placed upon catalytic activity of the walls of the reactoror reactor components.

Various means known to the art can be utilized for establishing intimatecontact of the reactants, i.e., olefin and molecular oxygen in thesolvent, for example, by stirring, sparging, shaking, vibration,spraying or other vigorous agitation in the reaction mixture. Thevigorous agitation of the reaction mixture effects not only intimatecontact of olefin and oxygen, but also facilitates removal of the heatof reaction to suitably oriented heat exchangers. It is to be noted,also, that the exothermic nature of the olefin oxidation is such thatvery small or negligible amounts of heat need be applied to the reactionsystem in order to maintain the desired temperature of operation, hence,reaction temperature is adequately maintained by suitable design andproper use of heat exchange components.

As noted above, no added catalysts are required in the presentinvention. The usual oxidation catalysts can be tolerated althoughusually no significant benefit accrues from their use because the olefinoxidations proceed in such facile manner in the solvents of the instantinvention. Oxidation catalysts such as platinum, selenium, vanadium,manganese, silver, cobalt, chromium, cadmium and mercury in metallic orcompound form, preferably as oxide or carbonate or as soluble acetatesor carboxylates may be present singly or mixed in gross form supportedor unsupported or as finely-divided suspensions or in solutions in thesolvent.

It should also be noted that since olefin oxidations according to thisinvention proceed at such a rapid rate after a brief induction period noinitiators, accelerators, or promoters are required, but these may beused to shorten or eliminate the brief induction period after which noadditional initiator, promoter or accelerator need be added. Suitableinitiators, accelerators or promoters include organic peroxides such asbenzoyl peroxide, tertiarybutyl hydroperoxide, di-tertiary-butylperoxide; inorganic peroxides such as hydrogen and sodium peroxides;organic peracids such as peracetic and perbenzoic acid or various otherperoxidic derivatives such as the hydrogen peroxide and hydroperoxideaddition products of ketones and aldehydes. Also useful as initiators,promoters, or accelerators for the purpose of reducing the time of theinduction period, but following which induction period no more need beadded, are readily oxidizable materials such as aldehydes, such asacetaldehyde, propionaldehyde, isobutyraldehyde and the like and etherssuch as diethyl ether, diisopropyl ether, and the like.

The reaction mixtures to be used in carrying out the process of theinstant invention may be made up in a variety of ways. Exemplarycombinations are the olefin and/or oxygen premixed with the solvent, theolefin premixed with the solvent, suitably up to 50% by weight and,preferably, from 10% to 45% by weight of the solvent, and the oxygenadded thereto. The solvent-to-olefin molar ratio will .vary from 1 to10. The oxygen-containing gas may be introduced into the olefin-solventmixture incrementally or continuously. Or, the reactor may be chargedwith solvent and the olefin and oxygen gas may be introducedsimultaneously through separate feed lines into the body of the solventin a suitable reaction vessel. In one embodiment the olefin andoxygen-containing gas mixture is introduced into the solvent in acontinuously stirred reactor, under the conditions of temperatures andpressures selected for this particular olefin. Suitable olefin to oxygenvolumetric ratios are within the range of l to up to to 1. Feed rates,generally, of oxygen or oxygen-containing gas may vary from 0.5 to 1500cubic feet per hour or higher and will largely depend upon reactor sizewithin production quantity desired. The oxygen input is adjusted in suchmanner as to allow virtually complete usage of oxygen, thereby keepingthe oxygen concentration in the off-gas above the reaction mixture belowabout 1%. This safeguard is necessary in order to prevent a hazardousconcentration of explosive gases. Proper adjustment of feed rates is ofimportance in order that the olefin not be stripped from the liquidphase, thus reducing its concentration, hence reducing the rate ofoxidation of the olefin which would result in lower conversions per unittime of olefin to olefin oxide. The solvents used herein represent thepredominant constituent in the reaction mixture, with respect to allother constituents, including reactants, oxidation products andby-products. By predominant is meant enough solvent is always present toexceed the combined weight of all other constituents. In other words,the reaction mixture comprises major amounts of the solvent and minoramounts of all other constituents with respect thereto.

The oxidation products are removed from the reactor as a combined liquidand gaseous effluent containing the olefin oxide, unreacted componentsand by-products, by properly adjusting conditions of temperature andpressure and by adjustment of a let-down system, or the entire reactionmixture containing the oxidation products is removed from the reactor.Conventional techniques for separation of desired product includingdistillation, fractionation, extraction, crystallizations and the like,are em ployed to effect separation of the desired olefin oxide. Oneprocedure comprises continually removing the liquid efiluent from thereaction zone to a distillation column and removing various fractions ofproducts contained therein, in eifect, a fractionation to obtain theolefin oxide. From such suitable fractionation process the solvent isrecovered and is recycled to the reaction zone.

The invention will be more fully understood by reference to theillustrative specific embodiments presented below.

A modified cylindrical Hoke high pressure vessel is employed for thebatch-type oxidations described below. A high pressure fitting waswelded to the vessel near one end to serve as gas inlet, and a blockvalve with rupture disc was attached to this fitting with a one-quarterinch high pressure tubing goose-neck. A thermocouple was sealed into oneend-opening of the vessel. The solvent and initiator (if any employed)are then charged through the other end-opening which is then sealed withthe plug. The olefin is then charged to the desired amount, asdetermined by weight dilference, that is, the olefin, if normallygaseous, is charged under pressure, and if normally liquid, may becharged into one of the end openings along with solvent, and the chargedvessel is affixed to a bracket attached to a motor driven eccentricwhich provides vertical vibrational agitation. The tubular Hoke vesselis clamped in a horizontal position in order that the maximum agitationof contents ensues. This vibrating reaction vessel can be immersed in ahot bath for heating to reaction temperatures and removed, then immersedin a cold bath to quench to room temperature.

EXAMPLE I To a 150-ml. pressure vessel fitted with a thermocouple,rupture disc and gas inlet tube was charged 25.96 g. of methyl benzoatecontaining 0.20 g. of acetaldehyde and 6.20 g. of propylene. The reactorwas sealed,

mounted on an agitator assembly and immersed in an oil bath maintainedat 200. When thermal equilibrium was reached, oxygen was admitted to thereactor at 415 p.s.i.g. total pressure. After two and one-half minutesreaction time, an additional p.s.i.g. oxygen pressure was added to thesystem making a total overpressure of 300 p.s.i.g. with respect to theinitial autogeneous reactor pressure (215 p.s.i.g.) at 200 C. A maximumtemperature of 234 C. was reached during the oxidation which startedimmediately upon introduction of the oxygen. After a reaction time offive minutes, the addition of oxygen to the system was stopped and thereactor was immersed in a cold water bath.

Vapor phase chromatographic analyses of the reactor contents showed40.0% propylene oxide yield among oxygenated products formed at a totalconversion of propylene of 29.1%.

EXAMPLE II To a pressure reactor of the type discussed above is charged25 g. of methyl benzoate containing 0.1 g. of acetaldehyde and about 5.0g. of ethylene. The sealed reactor is attached to the agitator assemblyand immersed in a hot oil bath at 200 C. When thermal equilibrium isreached within the reactor, oxygen is introduced to a total overpressureof 300 p.s.i.g. The oxidation is carried on for about seven minutes,then terminated as in the above example. Analyses indicate a 12%conversion of ethylene to oxygenated products including a 25% yield ofethylene oxide.

EXAMPLE III To a pressure reactor similar to the above type is charged30 g. of methyl benzoate, 0.15 g. acetaldehyde and about 8 g.2-methyl-2-butene. The sealed reactor is attached to an agitatorassembly and immersed in an oil bath at 160 C. When thermal equilibriumis reached within the reactor, an oxygen overpressure of 100 p.s.i.g. isintroduced to initiate the reaction followed after a 2 minute intervalby an additional 50 p.s.i.g. overpressure of oxygen. After a totalreaction period of about 10 minutes, oxygen addition is ceased, and thereactor is cooled in a cold water bath. Analyses indicate a 43%conversion of olefin to oxygenated products with the major product being2-methyl-2,3-epoxybutane obtained in 46% yield.

EXAMPLE IV To a 1-liter top-stirred stainless steel reactor is chargedabout 119 g. of propylene, 290 g. of methyl benzoate, and 3 ml. ofacetaldehyde. The reactor is heated to 180 C. and oxygen addition isinitiated. The oxidation begins almost immediately as evidenced by arise in temperature from heat of reaction. The oxidation is run forforty minutes with a final temperature and pressure of 203 C. and 1150p.s.i.g., respectively. There is obtained about 129 g. of liquidoxygenated products derived from propylene of which propylene oxide isthe major constituent.

EXAMPLE V To a Hoke pressure vessel as described is charged 25 g. ofmethyl benzoate, 0.1 g. acetaldehyde and about 5 g. styrene. The sealedvessel is attached to an agitator assembly and immersed in an oil bathat C. After thermal equilibrium is reached within the reactor oxygen isadded gradually over an approximate 10 minute reaction period to a totaloxygen pressure of 250 p.s.i.g. The reaction is quenched as above toobtain a 55% conversion of olefin to oxygenated products among whichstyrene oxide is a major constituent.

EXAMPLE VI To a pressure reactor is charged methyl benzoate,acetaldehyde initiator and butadiene. The sealed reactor is attached toan agitator assembly and immersed in an oil bath at C. When thermalequilibrium is attained, oxygen is introduced to a total pressure of 200p.s.i.g. over a reaction period of about 8 minutes. The oxygen is shutoff and the reactor is cooled in a cold water bath. Analyses indicate a65% conversion to oxygenated products containing butadiene oxide in 22%yield.

EXAMPLE VII This example exemplifies a continuous operation for olefinoxidation using methyl benzoate as the reaction medium.

A 1.0-liter stirred stainless steel reactor is employed, fitted withthree feedlines to introduce propylene, oxygen and methyl benzoatesolvent into a bottom inlet in the reactor. A product over-flow pipedrains gaseous and liquid product continuously into a product separationsystem.

Using methyl benzoate as solvent, the reactor is heated to 200 C. andpropylene is charged to about 20% by weight of the solvent. The reactionis initiated by incremental additions of oxygen, then the threereactants are metered into the reactor as the oxidation products arecontinuously removed. In a typical run, the reactants are added at aboutthe following hourly rates: propylene, 500 g, oxygen, 300 g., methylbenzoate, 4400 g. At a steady reaction state with reactor residence timeof about 4 minutes, the conversions are, approximately, propylene 48%,oxygen 97% and propylene oxide yield is approximately 48%.

EXAMPLE VIII To a pressure reactor of the type discussed above ischarged 25 g. of 1,1-dimethylbu tyl benzoate containing 0.1 g. ofacetaldehyde and about 5.0 g. of ethylene. The sealed reactor isattached to the agitator assembly and immersed in a hot oil bath at 200C. When thermal equilibrium is reached within the reactor, oxygen isintroduced to a total overpressure of 300 p.s.i.g. The oxidation iscarried on for about seven minutes, then terminated as in the aboveexamples. Analyses indicate a 12% conversion of ethylene to oxygenatedproducts including a 25% yield of ethylene oxide.

EXAMPLE 1X To a pressure reactor similar to the above type is charged 30g. of 1,1-dimethyl triohloroethyl benzoate, 0.15 g. acetaldehyde andabout 8 'g. of 2-methyl-2-butene. The sealed reactor is attached to anagitator assembly and immersed in an oil bath at 160 C. When thermalequilibrium is reached within the reactor, an oxygen overpressure of 200p.s.i.g. is introduced to initiate the reaction followed after a 2minute interval by an additional 100 p.s.i.g. overpressure of oxygen.After a total reaction period of about minutes, oxygen addition isceased, and the reactor is cooled in a cold water bath. Analysesindicate a 43% conversion of olefin to oxygenated products with themajor product being 2-methyl-2,3epoxybutane obtained in 46% yield.

EXAMPLE X To a 1-liter top stirred stainless steel reactor is chargedapproximately 119 g. of propylene, 296 g. of neopentyl benzoate, and 3ml. of actaldehyde. The reactor is heated to 180 C. and oxygen additionis initiated. The oxidation begins almost immediately as evidenced by arise in temperature from heat of reaction. The oxidation proceeds forabout forty minutes with a final temperature and pressure of 200 C. and1100 p.s.i.g., respectively. There is obtained approximately 139 g. ofliquid oxygenated products of which propylene oxide is the majorconstituent.

EXAMPLE XI To a Hoke pressure vessel as described above is charged 25 g.of 1,1,3,3-tetramethylbutyl benzoate, 0.1 g. actaldehyde and about 5 g.styrene. The sealed vessel is attached to an agitator assembly andimmersed in an 10 oil bath at C. After thermal equilibrium is reachedwithin the reactor oxygen is added gradually over about 10 minutereaction period to a total oxygen pressure of 250 p.s.i.g. The reactionis quenched as above to obtain an approximate 55% conversion of olefinto oxygenated products among which styrene oxide is a major constituent.

EXAMPLE XII To a pressure reactor is charged 1,1-dimethylpropylbenzoate, acetaldehyde initiator and butadiene. The sealed reactor isattached to an agitator assembly and immersed in an oil bath at C. Whenthermal equilibrium is attained, oxygen is introduced to a totalpressure of 200 p.s.i.g. over a reaction period of about 8 minutes. Theoxygen is shut off and the reactor is cooled in a cold water bath.Analyses indicate a 55 conversion of oxygenated products containingbutadiene oxide in about 22% yield.

EXAMPLE XIII To a 150-ml. pressure vessel fitted with thermocouple,rupture disc and gas-inlet assembly was charged 25.16 g. of ethylbenzoate, 0.13 g. of acetaldehyde (to reduce the induction time) and6.07 g. of propylene. The reactor was sealed, mounted on an agitatorassembly and immersed in a polyethylene glycol bath maintained at C.When thermal equilibrium was reached the autogenous pressure of thevessel was 217 p.s.i.g. Oxygen was introduced at 100 p.s.i.g.over-pressure, then increased slowly until 460 p.s.i.g. total pressurewas reached. A maximum temperature of 213 C. was reached, and at fourminutes the oxygen was turned off and the reactor was immersed in a coldwater bath. Analyses by vapor phase chromatography of the reactorcontents indicated an overall conversion of propylene of 15.1% tooxygenated products, among which propylene oxide was obtained in 39.9%yield.

EXAMPLE XIV To the Hoke pressure vessel described above was charged23.48 g. of isopropyl benzoate, 0.13 g. of acetaldehyde (to reduce timeof induction period) and 6.14 g. of propylene. The vessel was sealed,attached to the agitator assembly of the oxidation apparatus andimmersed in a polyethylene glycol bath maintained at 190 C. Anautogenous pressure of 200 p.s.i.g. developed when thermal equilibriumwas reached. Oxygen was introduced at 310 p.s.i.g. total pressurewhereupon oxidation commenced immediately. The oxygen feed pressure wasslowly increased to 452 p.s.i.g. total pressure and a maximumtemperature of 203 C. was reached. At five minutes, the oxygen wasturned off and the vessel was immersed in a cold water bath. Vapor phasechromatographic analyses of the reaction mixture indicated a 10.2%conversion of propylene to oxygenated products amlong which propyleneoxide was obtained in 58.1% yie d.

Various other modifications of the instant invention will be apparent tothose skilled in the art with-out departing from the spirit and scopethereof.

Iclaim:

1. Process for the preparation of olefin oxides which comprisesoxidizing an epoxidizable olefinically unsaturated hydrocarbon compoundhaving up to 18 carbon atoms with molecular oxygen at a temperaturewithin the range of from 50 C. to 400 C. and pressures within the rangeof from 0.5 to 150 atmospheres in a liquid reaction medium consistingessentially of an ester selected from the group consisting of benzoicacid esters having the formula:

and mixtures thereof, wherein R R and R are selected from the groupconsisting of hydrogen, straight chain alkyl and haloalkyl groups havingfrom 1 to 4 carbon atoms and straight chain alkyl and haloalkyl groupshaving from 1 to 4 carbon atoms having as substituents on other than theterminal carbon atom thereof a member selected from the group consistingof alkyl and haloalkyl groups having from 1 to 4 carbon atoms.

2. Process according to claim 1 wherein the oxidation occurs in theabsence of added catalysts.

3. Process for the preparation of propylene oxide which comprisesoxidizing propylene with molecular oxygen at a temperature within therange of from 140 C. to 250 C. and a pressure Within the range of from10 to 100 atmospheres :in a liquid reaction medium as described in claim1.

4. Process according to claim 3 wherein said reaction medium consistsessentially of methyl benzoate.

5. Process according to claim 3 wherein said reaction medium consistsessentially of ethyl benzoate.

6. Process according to claim 3 wherein said reaction medium consistsessentially of isopropyl benzoate.

7. Process according to claim 3 wherein said liquid reaction mediumconsists essentially of a mixture of said benzoic acid esters.

12 8. Process according to claim 7 wherein said liquid reaction mediumconsists essentially of a mixture of methyl benzoate and isopropylbenzoate.

References Cited by the Examiner OTHER REFERENCES Bergmann, TheChemistry of Acetylene and Related Compounds, page 20, IntersciencePublishers Inc., New York (1948).

Durrans, T. H., Solvents, 7th ed. (1957), pp. XV and 128-147.

WALTER A. MODANCE, Primary Examiner.

IRVING MARCUS, JOHN D. RANDOLPH,

NICHOLAS RIZZO, Examiners.

JAMES A. FRIEDENSON, NORMA MILESTONE,

Assistant Examiners.

1. PROCESS FOR THE PREPARATION OF OLEFIN OXIDES WHICH COMPRISESOXIDIZING AN EPOXIDIZABLE OLEFINICALLY UNSATURATED HYDROCARBON COMPOUNDHAVING UP TO 18 CARBON ATOMS WITH MOLECULAR OXYGEN AT A TEMPERATUREWITHIN THE RANGE OF FROM 50*C. TO 400*C. AND PRESSURES WITHIN THE RANGEOF FROM 0.5 TO 150 ATMOSPHERES IN A LIQUID REACTION MEDIUM CONSISTINGESSENTIALLY OF AN ESTER SELECTED FROM THE GROUP CONSISTING OF BENZOICACID ESTERS HAVING THE FORMULA: